Scaling Pinterest - From 0 to 10s of Billions of Page Views a Month in Two Years

http://highscalability.com/blog/2013/4/15/scaling-pinterest-from-0-to-10s-of-billions-of-page-views-a.html?utm_source=feedly

by aespinoza • 13 years ago

261 45 13 years ago

highscalability.com

RyanZAG• 13 years ago

I'm fairly amazed by some of the choices - in particular the single huge user table that is hit on every profile page view to map url to shard. I'm guessing it has hot backups and similar - but wow - talk about a single point of failure. I guess having it like that actually makes it easier. If it fails, it should be trivial to get it back up quickly on a backup machine.

The whole setup seems a lot simpler than nearly every 'web scale' solution I've heard discussed.

EDIT: I'm not saying that is a bad thing - it's a good thing. Most of the articles around scaling on HN often deal with very complex Cassandra style technical solutions. This article is the opposite with a very 'just do it the simplest way' feel to it. One big mysql table for all users (probably with some memcache in front) is the sort of thing you can put together in an hour or two - yet it is the very core of their system.

I (and I bet a lot of other engineers reading HN) try to focus too much on perfect implementations - if someone asked me to design the shard look-up for something as heavily hit as this, I'd probably reach for a distributed in-memory DB with broadcasted updates - and I'd probably be wrong to do so. The mysql/memcache approach is just going to be simpler to keep running.

coolsunglasses• 13 years ago

You don't really want to get into the alternatives. It's pretty common to shard everything but the core user data (email, PBKDF2, username) and scale that with slaves and vertical upgrades. SSDs can take you a long way if you're fastidious about offloading everything else off the machine responsible for keeping user accounts consistent.

The alternatives aren't nice.

aespinoza• 13 years ago

I agree. Usually it is better to scale vertically on the user data. Even if it seems painful. The alternatives like partitioning are not really that easy either. There is pain involved as well.

I think, of the existing solutions, one is not better than the other. The choice in the end is which one fits best with your team and infrastructure, and specially which disadvantages are you willing to put up with.

chiph• 13 years ago

Since they're MySQL pros, they could put that on a MySQL Cluster and get high availability (up to 30 or so machines in the cluster, use a larger replica count, on top of drive mirroring, etc.) Also, it's a read-heavy workload, so hide it behind memcached.

jokull2• 13 years ago

That’s not what they’re doing. They are sharding horizontally on the user. ID’s are 64 bits with the db location (logical shard id) in the first 16 bits. This will allow anyone with an ID to go to the right db for querying, granted they have logical to physical shard mappings.

js2• 13 years ago

From the article:

User table is unsharded. They just use a big database and have a uniqueness constraint on user name and email. Inserting a User will fail if it isn’t unique. Then they do a lot of writes in their sharded database.

Get the user name from the URL. Go to the single huge database to find the user ID.

I believe the parent is correct.

jacques_chester2• 13 years ago

One table for users is a no-brainer. The outer limit on table size is ~7 billion rows.

And that's just not a very big table these days.

mcartyem2• 13 years ago

This might be a silly thing to ask, but why don't they save their data in flat files on a shared filesystem?

They wouldn't need Memcached, since the OS caches files anyway; replication with rsync becomes easy; they don't need transactions anyway; and they wouldn't have so much software to manage.

hboon2• 13 years ago

Storing, tracking and managing billions of tiny files directly on a file system is a nightmare

garydarna• 13 years ago

Great article, thanks for sharing.

nasalgoat• 13 years ago

I wonder if their dislike for Cassandra is based on previous versions pre-2.0. From my perspective of looking at it as it stands now, it's pretty compelling.

zcam• 13 years ago

You probably mean pre 1.2 as 2.0 isn't there yet.

cnlwsu2• 13 years ago

DataStax did call it 2.0 and now 3.0

bloodredsun5• 13 years ago

Not if you want strong consistency. Cassandra's performance sucks in comparison with the likes of MongoDb or Couchbase when reading with strong consistency since the clients have no idea of the server topology.

cnlwsu2• 13 years ago

umm what? Cassandra is just as fast/faster (depending on both configurations and load) compared to MongoDB with consistant read/writes. Definitely with writes but reads get tricky.

anderspetersson• 13 years ago

great talk, inspired me to simplify the tech stack.

Pyres looks like a good alternative for Celery in the Python world when you don't need Celery's cron-like features.

rikacomet• 13 years ago

A simply awesome article, that I would refer to back and again, can someone please refine this with his comments as well. I mean it would be really helpful to point out any mistakes Pinterest did, at any point, what I want to know is, what could they have done better. Also, business is a dynamic environment, so somethings might have changed, so can someone please also point out, if something was right when pinterest did it, but now there are better alternatives. Thanks a lot in advance. I would be really reading many of the comments properly.

~Rika

fotcorn• 13 years ago

Does someone now what programming language and framework they use? Still Python+Django? PyPy?

goronbjorn• 13 years ago

From what I've read, it's Python and "heavily modified" Django. I recall one of their engineers saying that, if they were to do it again, they would've gone with a more lightweight Python framework because of how many heavy modifications they made.

misiti3780• 13 years ago

I have read that also (multiple times actually) and the statement never made sense to me - of course in hindsight you would start with something like Flask because you ran into all of the scaling problems with Django, but there would be no way to fix these problems before they occurred - and if you did try to fix them before they would occurred, it would be premature optimization. It seems like a example of what Taleb's calls the "Narrative Fallacy"

http://cij.inspiriting.com/?p=364#

dlhavema• 13 years ago

Very cool, I thought pinterest came out of nowhere and is now everywhere, but i didn't realize how fast they did it and how large they've grown.

thanks for posting!

bloodredsun5• 13 years ago

What is most interesting to me is that in many ways they have reinvented Couchbase. I think that the only reason they didn't go with this technology was the financial cost for their scale was too high.

cagenut• 13 years ago

I really like how when you look at it, most of their scaling was removing things from the environment and really honing the platform down to what it needed to be.

dmourati• 13 years ago

More specifics about the decision to dump MongoDB would be extremely useful.

sontek• 13 years ago

How does SOA improve scaling? I've never had to build anything as big as pinterest and it seems interesting to me.

I don't quite understand how it reduces connections. If you have your front-end tier connecting to your service tier, you'll still have the same amount of requests going to the database, just with a little middle-man... If I understand correctly?

aaronbrethorst• 13 years ago

I'm no expert, but hopefully by abstracting out different services from your core app and making them available through some connection protocol (Thrift, a message queue, http, whatever) you can more easily scale up and scale out systems that become hotspots, and consumers of that service will never be any the wiser, since they only interact with it through the published API.

Looking at it another way, when I talk to the GitHub API, I have no idea what sort of database I'm ultimately talking to. Their interface abstracts away all of that complexity. Each request they receive from me might be handled by a different machine for all I know. It makes no difference.

bloodredsun5• 13 years ago

By itself SOA doesn't do anything but it does free you up to do other things that allow you to scale like read-write separation and event driven or fan-out caching. One of the most important thing SOA does is that it quickly stops you from doing dirty hacks that work right now but are killers for future work. It's encapsulation at the application level

arocks• 13 years ago

Service orientation allows specialization of architectural components. If you want to build on scale, it is easier to replicate specialized components than a generalized one. It also benefits from better fault tolerance.

Additionally, services layer forms an interface between the client and service provider, which makes it easier to scale.

jacques_chester2• 13 years ago

> Architecture is doing the right thing when growth can be handled by adding more of the same stuff. You want to be able to scale by throwing money at a problem which means throwing more boxes at a problem as you need them. If you are architecture can do that, then you’re golden

My understanding is that the term of art is horizontal scalability.

jnankin3• 13 years ago

2 questions: 1) What do they do with the Pinterest-generated ID? Do they store it with each row in addition to the local ID? 2) Why randomly select a shard? Shouldn't you do this based on DB size across all boxes, or at least based on physical space left across all boxes?

jnankin3• 13 years ago

Oops, 1 is directly mentioned in the talk.

yashh2• 13 years ago

We decompose 64 bit ids to shard_id, type and local_id. We connect to the shard go to the table and read the local_id.

We randomly select a shard for a new user only. Ofcourse we capacity plan this and open new shards and even out users eventually.

jnankin3• 13 years ago

what happens if 1 shard contains a whole slew of large companies (macy's, gap, etc), or over time users on one shard grow to the point that they cannot be contained within one physical machine? Are they just assuming that this will be very unlikely?

yashh2• 13 years ago

No not at all. We already have this problem. Right now we are able to take the DB hit but we will eventually attack this problem from cache perspective. We will have replicated caches for this scenario. In worst case if a shard is overloaded we stop creating new users in it and put it on a dedicated physical machine. I dont think we will let the situation get there.

Scaling Pinterest - From 0 to 10s of Billions of Page Views a Month in Two Years

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